Single radio voice call continuity (SRVCC) is a voice over Long-Term Evolution (LTE) (VoLTE) service continuity solution proposed by the 3rd Generation Partnership Project (3GPP). The solution is mainly used to ensure voice service continuity when a voice service of VoLTE user equipment (UE) is handed over to a 2/3G circuit-switched (CS) domain.
FIG. 1A to FIG. 1C show a signaling interworking diagram of SRVCC in the prior art. As shown in FIG. 1A to FIG. 1C, in an SRVCC process, a mobile switching center (MSC) initiates an initial session handover process to an Internet Protocol (IP) multimedia subsystem (IMS) (step a1), and triggers the IMS to perform session handover and remote leg update (step a2), so as to hand over a voice session to a circuit-switched domain; on an IMS side, the session handover is completed, an IMS side access leg resource is released (step a3), and a session termination message is sent to a Policy and Charging Rules Function (PCRF) (step a4); the PCRF sends a re-authentication request message to a gateway device (step a5), where the message is used to instruct the gateway device to delete a voice bearer (that is, a bearer whose Quality of Service (QoS) Class Identifier (QCI) is equal to 1), and the gateway device is a gateway device that integrates a service gateway (SGW) and a packet data gateway (PGW); further, the gateway device sends a bearer deletion request to a Mobility Management Entity (MME) (step a6) to request deletion of a voice service bearer. Likewise, in the SRVCC process, the VoLTE user equipment hands over an original voice service from an evolved packet system (EPS) network to a 2/3G network. After the handover is completed, the MME in the EPS network (that is, on an EPS side) sends a bearer deletion instruction message to the gateway device (step b12), where the message is used to request deletion of a bearer that is previously used for bearing a voice service, and the bearer refers to a bearer whose QCI is 1; after deleting a voice service bearer, the SGW/PGW initiates a bearer deletion request to the MME (step b13); after the voice service bearer is deleted, the MME sends a bearer deletion response to the SGW/PGW (step b14).
Based on the foregoing technical solution, in the SRVCC process, an original voice service bearer whose QCI is equal to 1 is deleted on both the EPS side and the IMS side. In addition, in the prior art, a time sequence for performing bearer deletion on the two sides is not defined. That is, in step a5, the gateway device receives the re-authentication request message sent by the PCRF and needs to perform an operation of deleting the voice service bearer, while in step b12, the MME sends the bearer deletion instruction message to the gateway device, and the gateway device also performs an operation of deleting the voice service bearer, which causes a conflict in the SRVCC process, and may even cause handover termination on the EPS side, and consequently the voice service is interrupted.